How to figure out the equation of the perpendicular bisector of a line when the end points of the line are given?

First find the equation of the line, Ill use the first one as an example:

(-5,10)  , ( -9,2)

To work out the gradient:



So the gradient of the line is 2

The midpoint of the line is 
The gradient of the inverted line is -0.5 as it is the negative reciprocal of the gradient of the first line.
Here, we work out the equation of the bisector.